1. Field of the Invention
The present invention relates to a mechanism for an optical system, and in particular to an optical system in a scanner.
2. Description of the Prior Art
In a typical scanner, two moving optical modules with mounted reflecting mirrors are used. A scanning light source is placed in one module A scanning light ray is reflected by a mirror in the second module to a light sensor that is fixed on the frame of the scanner Both modules move along a same track. It is desirable to maintain a fixed optical path length between the light source and the light sensors This can be accomplished by moving both modules together, but with different speeds. A speed ratio of 1:2 is often chosen. The difference in speed is obtained by choosing different diameters of rollers that drive a conveying belt for the two optical modules.
In a traditional scanner, the motor for driving the optical modules is mounted on the frame of the scanner. When this driving motor operates, the motion of the driving motor may cause vibration of the frame of the scanner and create a great deal of noise. Such a noise is undesirable.
It is also desirable to miniaturize the size of a scanner.
It is an objective of this invention to reduce noise of the dual speed modules. Another objective of this invention is to reduce the thickness and hence the size of a scanner with dual speed modules.
These objectives are achieved by mounting a driving motor on one of the modules Since the motor is not directly mounted on the frame, the frame does not vibrate as violently, and the noise is reduced. In addition, by not mounting the motor on the frame, no space is required for the motor in vertical or horizontal directions. Thus, the frame of the scanner can be made thinner or narrower, and hence smaller.
Two moving optical modules are used A scanning light beam is emitted from a first module and directed toward a second optical module, which is pulled by the first optical module. The light beam in reflected by a mirror in the second optical module toward a light sensor placed on the other side of the first optical module. As a scanning light in the first optical module moves toward the light sensor, the separation between the first optical module and the second optical module is made, to increase such that the second optical module moves by one half the distance of the first optical module. In so doing, a light path traversed by the scanning light beam is maintained constant as the scanning light source scans. This mechanism is implemented by using two sets of belts moving at two different speeds: a first belt pulling the first optical module at a higher speed, and a second belt separating the two modules at a slower speed.
The second optical module is pulled by the second belt by a second driving wheel toward the first optical module by means of the second belt looping from the first optical module through the second driving wheel to a point at the right side wall of the frame. When the second driving wheel rotates in the same clockwise direction as a first driving wheel, the second optical module is pulled by the first optical module, but at a reduced speed due to lengthening of the separation between the first optical module and the second optical module, which tends to move toward the left side but is overcome by a right side pull from the first optical module. The net pull results in a reduced rightward speed of the second optical module.